This invention relates to a method of and apparatus for developing a signal containing information as to the characteristics of at least one moving element situated internally of a living body. A principal application of the invention is to obtaining information as to the characteristics of motion of the heart in a human body, but it is to be understood that the invention may be applied to the generation of a signal containing information as to the characteristics of some other inaccessible moving element of a living organism.
Such elements are normally inaccessible to the obtaining of such information in the sense that they are not visible by the use of ordinary light rays. The employment of penetrating radiation such as X-rays often requires that the element concerned be brought into contact with a medium such as a barium salt before such element can be resolved from surrounding tissue, and the latter technique is not applicable to many elements of the human body including the heart.